Tim smashes through a wall with a sledgehammer with Jill on the other side, just like in the intro.
The title refers to the three witches' dialog in Shakespeare's 'Macbeth' (Act IV, Scene I): "Double, double toil and trouble; Fire burn and cauldron bubble."
At one point, Tim says, "Women are like a Mr. Potato Head." However, Mr. Potato head later appeared in Toy Story, in which Tim Allen voiced Buzz Lightyear.